function postRequest(url, parameters, callback) {
	var request = false;
	if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
		request = new XMLHttpRequest();
		request.open('POST', url, true);
		request.setRequestHeader("Content-type",
				"application/x-www-form-urlencoded");// TODO fix?
		// which headers are needed?
		// http_request.setRequestHeader("Content-length", parameters.length);
		// http_request.setRequestHeader("Connection", "close");
		request.onreadystatechange = function() {
			if (request.readyState == 4) {
				if (request.status == 200) {
					callback(request);
				}
			}
		};
		request.send(parameters);
	} else {
		//no ajax
	}
}